Processes for the recovery of cephalosporin C by means of reaction of the side chain amino group with acyl halides, alkyl isocyanates, aryl isocyanates and chlorocarbonates to give the corresponding derivatives are already known. See, for example, Belgian Pat. Nos. 758,800 and 807,171; U.S. Pat. No. 3,573,295 3,573,296; and German D.O.S. No. 2,157,693. These processes, however, present some disadvantages such as the use of noxious chemicals which are not easily handled in a large amount, troublesome procedures for the isolation and purification of the reaction products and only moderate recovery yields.